The sentence that contains a participle functioning as a verb is:
The blinking sign warns drivers of a sharp curve ahead.
In this sentence, "blinking" is a present participle that functions as an adjective describing "sign," while "warns" is the main verb. However, it seems you are looking for participles specifically as verbs.
If interpreted strictly with emphasis on participles functioning as verbs, it could be noted that all sentences have participles used adjectivally or as part of verb phrases, but the most clear example is "waiting" in the first sentence, which is part of the verb phrase "are waiting."
I apologize for any misunderstanding. The first sentence, "The students are waiting for the bus," features "waiting" as a participle in a verb phrase.